The present invention relates generally to the production of oil and water from a reservoir to limit the watercut or water coning effects, and particularly to a system that utilizes an array of sensors for sensing the oil and water interface to permit better control over the movement of that interface.
In some oil reservoirs, the oil production rate has been limited by the inability to produce oil devoid of water. In vertical wells, the upper limit of oil production rates has been limited by watercutting, sometimes referred to as water coning, where water is drawn into the oil zone perforations.
Water coning is caused by a hydraulic potential difference between the fluid in the perforations and in the aquifer. Basically, the radial pressure drop due to oil flow causes water to rise towards the oil perforations. The rise of water to the oil perforations may be limited by reducing the rate of oil production but this, of course, greatly limits the xe2x80x9ccleanxe2x80x9d oil production rate.
Attempts have been made to produce both oil and water from appropriately located oil perforations and water perforations to prevent the draw of water into the oil perforations. The water perforations are formed through the wellbore casing, and water is removed from the aquifer through the perforations at a rate that is estimated to reduce water coning. One problem in existent systems is the difficulty of controlling the production rates of oil and water to ensure that neither water coning nor oil coning into the water perforation occurs. Because there is no dependable way to determine the advent of water coning or oil coning, the production rates of oil and/or water are adjusted only when water is found in the produced oil or oil in the produced water. Once this occurs, however, the produced oil or water is no longer clean, and sometimes the coning effect is difficult to reverse.
According to the present technique, a sensor array is utilized at a downhole location across the oil-water interface. The sensors are designed to output signals from which the presence of oil or water may be determined. The outputs generated are used, for instance, either directly or in a model based on reservoir characteristics. The sensors permit detection of movement in the oil-water interface which, in turn, allows the production rate of oil and/or water to be changed in a manner that will compensate for the movement in the oil-water interface. Thus, the effects of water coning or oil coning can be detected and limited or reversed at an early stage of development.